<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .box>div{
      float: left;
      width: 33.3%;
      height: 100px;
      background: red;
      line-height: 100px;
      text-align: center;
      font-size: 20px;
      color: #fff;
      border-right: 10px solid;
      padding-right: 20px;
    }
  </style>
</head>
<body>
  <!-- <div>内容</div> -->
  <div class="box">
    <div>1</div>
    <div>2</div>
    <div>3</div>
  </div>
</body>
</html>